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Coffee Refractometer: What Does It Do and How to Use It

With the rise of specialty coffee came the rise of specialty coffee tools. Among them is the so-called coffee refractometer.

But what is this scientific gadget? How and why is it used? And most importantly, can it help you brew better coffee? Keep reading to find out!

What is a coffee refractometer?

A refractometer measures how light bends (aka refracts) as it moves between air and liquid. This gives us information about the properties of the fluid. The coffee measures the Total Dissolved Solids (TDS), allowing us to calculate the extraction yield (1).

What is TDS, you ask?

The dissolved solids in your morning brew are the roasted and ground coffee parts that dissolve in the brewing water; essentially, they’re the coffee in your coffee. Once you’ve measured the TDS, you can use this formula to calculate the extraction yield. However, most companies will do this with software.

Extraction Yield % = Brewed coffee (g) TDS (%) / Dose (g)

As we all know, the extraction has a huge impact on a coffee’s flavor, so it’s a useful bit of information to gather.

Experts found the ideal extraction yield for drip coffee to be between 18% and 22% in the past. The TDS percentage was between 1.15 and 1.35. However, as the quality of specialty coffee has improved, these numbers can be pushed even higher.

Why use a coffee refractometer?

Lately, refractometers are being used more and more by coffee roasters, beverage companies, and high-end coffee shops. Even the rare ultra-keen home brewer is jumping on board.

When coupled with a well-trained palate, they’re an excellent way to dial in a new coffee or perform quality control (QC), according to industry expert Chris Baca:

The refractometer is one of the best QC tools we have today in coffee, so you should use it.

Once you’ve brewed an exceptional cup of coffee, you can use the refractometer to measure its TDS and extraction yield. That way, you’ll know if you’ve reproduced it precisely in the future.

Using your tastebuds is still the most important way to optimize your coffee. 

But plotting TDS and extraction yield can help you get an idea of what corrections are needed if your coffee tastes off. Whether your coffee is too strong or weak, under extracted or over extracted can be hard to distinguish on taste alone.

Coffee Refractometer Graphic for Refraction

How do I use a coffee refractometer?

Even though all this scientific terminology sounds complicated, using a refractometer is very simple. In fact, the hardest part might be opening your wallet, as most run upwards of $500.

Just add a few drops of brewed coffee to the refractometer’s sample well, and it will report a TDS value. If you’re using espresso, it’s just slightly more difficult as you’ll have to filter it first.

Here’s a video demonstration from former World Brewers Cup champion Matt Perger:

Repeat this process using different recipes while tasting until you land on the most delicious cup. Then you’ll know the optimal extraction yield for your coffee.

The Verdict

Do you really need a coffee refractometer? Of course not. But if you have the budget and a scientific mind, it’s a fun way to learn more about your coffee and achieve more consistently delicious brews.

FAQs

To increase the TDS, there are several adjustments you can make to your coffee recipe. You can grind finer, increase the brew time, increase the water temperature, use higher pressure if you’re brewing espresso, or use turbulence when brewing filter coffee (2).

You don’t necessarily need a coffee specific refractometer, but they will be more accurate. More importantly, coffee refractometers come with the necessary software to make coffee-related calculations like TDS and extraction yield.

Under extracted coffee can taste sour and acidic, with a thin body and overall lack of flavor. Over extracted coffee can taste burnt or bitter and can overwhelm the palate.

  1. MacCuaig, S. (2016, March 11). Coffee Science: What Is TDS And Why Should You Care? Retrieved from https://perfectdailygrind.com/2016/03/coffee-science-what-is-tds-and-why-should-you-care/
  2. Korhonen, J. (2019, January 21). How to Measure Extraction of Coffee. Retrieved from https://www.baristainstitute.com/blog/jori-korhonen/january-2019/how-measure-extraction-coffee
Julia Bobak
I love trail running, rock climbing, coffee, food, and my tiny dog — and writing about all of them. I start every morning with a fresh Americano from my home espresso machine, or I don’t start it at all.

Comments

  1. Total Dissolved Solids (TDS), when testing drinking water, is shown in PPM (parts per million). Digital meters for water testing cost about $10-$15. Water fanatics use them all the time.

    Using one of these inexpensive devices, why can’t you get a reading for your brewing water, then take a reading of your brewed coffee, then subtract the water value to get your coffee value and use that number?

    Great water has a TDS value because the best water has certain essential trace elements that are needed and desired to make the water taste great. Distilled water is devoid of these minerals that make water great, and in fact, you need to put additives into distilled water to make it decent to drink. Distilled water is good for plants because they don’t want those minerals that we do, but you still have to charge it will something like a drop of plant food for the plant to be able to “drink” the water.

    Everyone’s water is a little different. So to get the coffee value, measure the water, get its value, then measure the brewed coffee for its value and subtract the water value. That will give you the coffee value alone. That is useful for a strict coffee extraction measurement.

    But you might want the overall value anyway, the coffee along with the desired minerals in the water.

    If you don’t care so much about having a value to use to be able to repeat the extraction in other places. Then to be consistent in your own home you can just use the combined water and coffee number. The coffee only number is useful if you go someplace else where the water is different. But at home, you don’t need to separate the coffee value from the water value. The quick and easy way is to use both together.

    In that case the process is even easier. You just measure the brewed coffee and forget about subtracting any minerals in the water. Just get a value for brewed coffee at your place and that is your standard. No need to get a number for just the coffee, although you might want to have that number for when you do use different water.

    You can probably just start using the PPM value instead of the % that you get from the refractometer. Just as there is a special % you look for using the refractometer, just look for the target PPM from your DTS meter. Using a very affordable TDS meter, you can get your PPM reading and just figure out what the PPM is for an ideal brew.

    Everyone can afford one of these digital TDS meters and they are easy to get on Amazon and other places.

    Reply

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